The P.I. of this application, a pediatrician currently completing a fellowship in Pediatric Genetics and Metabolism has expertise in the diagnosis and clinical management of genetic disorders and inborn errors of metabolism, one year's experience in molecular genetic analysis of human hereditary disorders and a strong interest in urea cycle disorders and their molecular biology. Using the new techniques of the polymerase chain reaction (PCR and denaturing gradient gel electrophoresis (DGGE), she has detected the first mutation described in a family with late onset ornithine transcarbamylase deficiency and used direct mutational analysis by DGGE for the first time in the prospective diagnosis of a genetic disorder. Under the guidance of her sponsors she will have the unique opportunity to combine clinical skills with the biochemistry and molecular biology necessary to integrate phenotypic, metabolic and genotypic aspects of urea cycle disorders. This application focuses on disorders of ornithine transcarbamylase (OTC) and carbamyl phosphate synthetase (CPS). New polymorphisms within or flanking the OTC and CPS loci will be identified using traditional Southern blot technology as well as PCR and DGGE and will be used to construct DNA haplotypes to mark parental alleles. DNA haplotype analysis will then be used to assess the accuracy of allopurinol-induced orotidinuria in the detection of OTS deficiency-carrier females. A combination of allopurinol testing and DNA haplotype analysis will be used to determine the frequency of new mutations in the OTC gene, and the parental origin of those mutations. DNA haplotype analysis will also be used to distinguish between germ-line mosaicism and favorable lionization in somatic carriers of OTC mutations in families in which multiple affected offspring have been born to allopurinol negative, phenotypically unaffected mothers. PCR and DGGE will be used to identify and characterize mutations in the OTC locus. It is hoped that mutation analysis will begin to answer questions concerning how the nature of specific mutations correlates with phenotype.